1. Field of the Invention
This invention relates to directional locking wheel casters.
2. Background Information
A typical shopping cart has four off-center axis wheels; two freely swiveling front wheels and two fixed straight rear wheels. As a result, the shopping cart can be easily turned and moved in a forward direction. However, due to the fixed rear wheels, the shopping cart cannot be easily pushed backward or sideways.
A hospital bed, a medical utility cart, and a luggage trolley typically include four freely swiveling off-center axis wheels. These transport items can be pushed in any direction, e.g., forward, backward and sideways. However, as all four wheels are free to swivel, these transport items are hard to maneuver in a straight direction while being pushed. They tend to swing to the left or right uncontrollably. For example, a hospital bed is routinely moved by two people; one in front to guide the front end in the desired direction and one in back to push it forward.
Attempts have been made to solve the above-described problems by employing a locking caster. See for example, U.S. Pat. Nos. 2,583,858; 5,040,265; and 5,263,226. The casters described in these patents have one or more deficiency rendering them unsuitable for solving the design problem. The deficiencies include (i) a locking mechanism that swivels together with the wheel, rendering the locking mechanism susceptible to physical damage, (ii) a spring exerting a constant pressure against the rotation wheel, resulting in premature wear of the wheel surface and failure of the locking mechanism if the wheel surface is not clean, and (iii) an unlocking mechanism that requires reversing direction of the wheel rotation.
The need exists for an improved directional locking caster to overcome the drawbacks of existing caster designs.